A number of processes have been proposed for continuous production of steel dating back to the 1860s. “Continuous” in this context has been used to describe processes which semi-continuously charge hot metal or scrap and deslag while periodically tapping steel into ladles. It has been used to describe processes which continuously utilize various vessels while continuously tapping steel into ladles, though in certain aspects there are interruptions somewhere in the melting, refining, or transporting operations. And it has been used to describe fully continuous processes which continuously transport steel from melting, through refining, to molding in a continuous caster without interruption in the flow of steel.
Continuous steelmaking processes have not received general acceptance in the industry because they could not compete with conventional steelmaking technology. Frequent improvements in basic oxygen furnaces (BOFs), electric arc furnaces (EAFs), ladle metallurgy furnaces (LMFs), and other secondary treatment facilities have provided production and quality flexibility perceived as more profitable than commercialization of new and risky continuous steelmaking processes which have been proposed, although some processes have been extensively tested.
Processes that resemble non-equilibrium CSTRs or PFRs in certain respects have suffered from lack of control and failure to promise substantially lower meltshop costs than conventional batch operations. Most of these processes have been designed to continuously utilize the equipment and to perform one major refining step (e.g., desulfurization) while tapping steel into a ladle as practiced in batch operations. The utilization of most batch reactors is close to one hundred percent, eliminating substantially any advantage of processes that are not fully continuous and do not completely prepare the steel for introduction to continuous casters.
A large number of continuous steelmaking processes were introduced in the 1960s just after the peak of the open hearth furnace (OHF) process and during the time of rapid BOF development and growth. The number of new continuous steelmaking processes declined after the 1960s as BOF and EAF steelmaking processes were optimized and improved through the introduction of LMFs. Today, BOF, EAF, and LMF are mature technologies operating close to optimum, allowing for only marginal future improvements in these processes. A major decrease in meltshop costs is therefore only possible with new, revolutionary processing.
U.S. Pat. No. 6,155,333 describes a scrap-based process which continuously charges scrap and continuously operates at near-equilibrium steady state conditions during melting, decarburization, and dephosphorization. However, the overall process is only semi-continuous because periodic tapping of the furnace interrupts the overall steady state operation.
In order to offset risks of investing in new technology, a new steelmaking process needs to have a potential to significantly reduce meltshop costs, and be reliable. There is a need, therefore, for a fully continuous process which can produce high quality steel at significantly lower cost with sufficient reliability and benefits to justify commercialization.